Process of making spherical powder grains



2,715,574 PROCESS OF MAKING SPHERICAL POWDER GRAINS Gilbert R. Cox, Creve Coeur, Mo., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Application June 14, 1951, Serial No. 231,647

14 Claims. (Cl. 52-20) This invention relates to the manufacture of propellent powders and more particularly to a process of manufacturing substantially spherical grains of smokeless powder.

Heretofore, spherical grains of smokeless powder have been made in accordance with the process disclosed in U. S. Patent 2,027,114, granted January 7, 193 6, to Olsen, Tibbitts and Kerone, in which globules of lacquer, composed of a smokeless powder base and a solvent, are suspended in a non-solvent medium and the globules solidified while thus suspended. As pointed out by Schaefer in U. S. Patent 2,160,626, there is often a tendency in the foregoing process for the non-solvent medium in which the globules are suspended to diffuse into the globules or to becomes emulsified therein. In addition, if the solvent is not entirely immiscible with the non-solvent medium, nonsolvent medium dissolved in or miscible with the solvent will be included within the lacquer globules when the globules are formed. As the solvent is removed from the globules of lacquer by vaporization, some non-solvent may remain therein and the resulting powder grains have a porous internal structure. Schaefer in the aforesaid patent discloses a method of controlling the porosity of the powder grain wherein the non-solvent medium without the globules is differentiated from the non-solvent medium within the globules in order to cause relative migration of the non-solvent medium within and without the globules. Such difierentiation can be accomplished by ineluding in the non-solvent medium some salt such as sodium sulfate. However, it becomes increasingly more ditlicult to make substantially non-porous or high density powder grains in accordance with such a process when solvents, such as methyl ethyl ketone, having increasingly greater solvency for the non-solvent medium, such as water, are utilized for the lacquer vehicle.

An object of this invention is to provide an improved method of making substantially non-porous spherical powder grains when a solvent is employed in which the non-solvent medium is partially soluble. Another object is to provide a novel method of controlling the porosity of substantially spherical powder grains. A still further and more specific object of this invention is to provide a process of controlling the quantity of non-solvent medium included in the globules of lacquer utilized in the I! manufacture of substantially spherical powder grains. Still another object of this invention is to provide a process of manufacturing substantially spherical powder grains even when solvents substantially miscible with the non-solvent medium are utilized.

The foregoing objects as well as others which will become apparent from the following description are accomplished in accordance with this invention, generally stated, by suspending globules of lacquer containing a smokeless powder base, a solvent therefor and a non-solvent diluent miscible with the solvent in a nonsolvent medium which is substantially immiscible with the non-solvent diluent, and then solidifying said globules while thus suspended. More specifically this invention contemplates a process of controlling the porosity of the spherical powder grains wherein the quantity of non-solvent medium within the globules of lacquer formed in the process is controlled by limiting the miscibility of the lacquer vehicle with the non-solvent medium by includii g a non-solvent diluent substantially miscible with the smokeless powder base solvent and substantially immiscible with the non-solvent medium in the lacquer vehicle. While no definite theory is known which com plete'ly explains the function of the non-solvent diluent in the lacquer vehicle, the solubility of the nonsolvent medium in the smokeless powder base solvent is reduced by the addition of a non-solvent diluent, and, generally, the more the diluent added the less the solubility. It is also appreciated that thenon-solvent diluent might also affect the interfacial tension of the solvent and nonsolvent medium. With the employment of the diluent, the non-solvent medium without the globules may be differentiated from that within the globules as disclosed by ,Schaefer in U. S. 2,160,626 in order to obtain even higher density powder grains.

Solvents and non-solvent diluents having a boiling point less than that of the non-solvent medium are preferred. It the non-solvent medium is water, solvents and non-solvent diluents having boiling points between about 50 C. and about 100 C. have been found particularly desirable. The actual composition of the lacquer vehicle which will give optimum results will of course vary with the solubility of the non-solvent medium in the smokeless powder base solvent utilized and the powder grain density desired. When methyl ethyl ketone, for example, is utilized as the solvent and water as the nonsolvent medium, as little as about 5% non-solvent diluent is sufiicient to produce high density powder having a specific gravity of 1.4 or more. Vehicles comprising as much as about toluene have been utilized to advantage in making high density powder from a smokeless powder base having a nitrogen content of about 12.6%. Amounts of non-solvent diluents of from about 5% to 20% may be utilized in the manufacture of high density powder from either pyro or gun-cotton grades of smokeless powder base; in order to obtain optimum results, the non-solvent diluent should be mixed with the smokeless powder base solvent prior to forming the lacquer. In most instances a ratio of about 2.5 to 6 parts vehicle to 1 part smokeless powder base forms a lacquer having the proper physical properties.

In order to further explain and clarify this invention, following is a typical embodiment thereof wherein a lacquer vehicle comprising a non-solvent diluent is used to advantage in the production of non-porous or high density spherical powder grains:

Approximately 65 parts nitrocellulose of about 12.6% nitrogen content are suspended in about 900 parts water. About 380 parts lacquer vehicle containing about methyl ethyl ketone saturated with water and about 5% toluene are added and the resulting mixture agitated until the nitrocellulose is completely dissolved. About 35 parts gum arabic dissolved in about parts water are added and agitation continued until the lacquer is completely dispersed in the water phase and the individual globules thus formed become substantially spherical. Approximately 35 parts sodium sulfate dissolved in about 80 parts water are then added and the lacquer vehicle removed from the lacquer globules by distillation while maintained in suspension in the water by means of gentle agitation. The solidified grains are later dewatered by filtering and oven drying. High density owder grains having a specific gravity between about 1.5 and 1.6 are produced in accordance with this process.

Instead of methyl ethyl ketone, other suitable solvents for the smokeless powder base such as ethyl acetate,

ethyl formate, isopropyl acetate, diethyl ketone and the like can be utilized in the foregoing embodiment. Likewise, other non-solvent diluents such as the liquid hydrocarbons xylene, benzene, pentane, hexane, heptane, octane, nonane, decane, undecane or dodecane or other compatible water immiscible diluents such as isopropyl ether, propyl ether, cyclohexane, methylcyclohexane, or the like can be utilized instead of toluene. If desired, other materials, for example, stabilizers such as diphenylamine, ethyl centralite and the like, deterrents such as dinitrotoluene, dibutylphthalate and the like and other modifying agents such as lead compounds, cyclotrimethylenetrinitramine, carbon black and the like may be included in the lacquer in accordance with the usual practice.

When the foregoing example is followed with the exception that the lacquer vehicle consists of methyl ethyl ketone saturated with water, low density powder grains having a specific gravity of about 1.3, 1.4 or less are produced.

From the foregoing description, it will be apparent to those skilled in the art that the invention accomplishes its objects and provides an improved method of producing substantially non-porous powder grains and a method of controlling the porosity of spherical powder grains wherein the quantity of non-solvent medium within the lacquer globules formed in the manufacture of spherical grains of powder is regulated.

While the foregoing embodiment has been described in detail, it is to be distinctly understood that various modifications of the procedure will occur to those skilled in the art and that the invention is not limited tothe specific embodiment hereinbefore set forth, except as indicated in the appended claims.

Having thus described the invention, what is claimed and desired to secure by Letters Patent is:

1. in the manufacture of powder grains by dispersing globules of smokeless powder base lacquer in a nonsolvent medium, the process of reducing the quantity of non-solvent medium dispersed Within said globules which comprises including in the lacquer a volatile liquid nonsolvent diluent which is substantially miscible with the lacquer solvent and substantially immiscible with the non-solvent medium.

2. In the manufacture of powder grains by dispersing globules of smokeless powder base lacquer in a nonsolvent medium, the process for making substantially non-porous powder grains from a lacquer containing a solvent which is at least partially miscible with the nonsolvent medium which comprises reducing the quantity of non-solvent medium dispersed within the lacquer globules by including a volatile liquid non-solvent diluent substantially miscible with the solvent and substantially immiscible with the non-solvent medium and differentiating the non-solvent medium without the globules from that within the globules.

3. The process of claim 1 wherein the lacquer has a boiling range between about 50 C. and 100 C. and the non-solvent medium is water.

4. The process of claim 1 wherein the solvent is methyl ethyl ketone, the non-solvent diluent toluene, and the non-solvent medium water.

5. The process of claim 4 wherein the non-solvent diluent is hexane.

6. The process of claim 2 wherein said globules are solidified in the presence of a protective colloid.

7. The process as set forth in claim 2 in which the amount of non-solvent diluent is within the range of about 5 per cent to about per cent of the lacquer vehicle.

8. The process as set forth in claim 7 in which the non-solvent medium without the globules is differentiated from that within the globules, and said globules are solidified in the presence of a protective colloid.

9. In the manufacture of substantially spherical powder grains by the process which involves dispersing globules of a smokeless powder base lacquer in a non-solvent medium and thereafter solidifying the globules while thus dispersed, the step of providing resulting powder grains with low porosity which comprises the inclusion in said lacquer of a volatile non-solvent diluent which is substantially miscible with the solvent in said lacquer and which reduces the solubility of said non-solvent medium in said lacquer.

10. The process of claim 9 in which said diluent is a liquid hydrocarbon and said medium is water.

11. in the manufacture of substantially spherical powder grains by a process which involves dispersing globules of a smokeless powder base lacquer in a non-solvent medium, the step which comprises including in said lacquer a volatile non-solvent diluent.

12. In the manufacture of powder grains by a process which involves dispersing globules of lacquer containing a smokeless powder and a solvent therefor in a non-solvent medium and thereafter solidifying the globules of lacquer while thus dispersed, the process for making substantially non-porous powder grains from a lacquer containing a solvent at least partially miscible with the non-solvent medium which comprises reducing the quantity of non-solvent medium dispersed within the lacquer globules by including therein a volatile liquid non-solvent for the smokeless powder base which is substantially miscible with the solvent and substantially immiscible with the non-solvent medium.

13. in the manufacture of powder grains by dispersing globules'of smokeless powder base lacquer in a nonsolvent medium partially miscible therewith and thereafter solidifying said globules, the method of reducing the miscibility of the lacquer with said medium which comprises including a volatile liquid non-solvent diluent in the lacquer.

14. In the manufacture of powder grains by suspending globules of a smokeless powder base lacquer in a non-solvent medium and solidifying the globules while thus suspended, the process for shaping and solidifying smokeless powder base lacquer into substantially spherical grains of propellent powder having a predetermined porosity which comprises dissolving the smokeless powder base in a volatile solvent for the smokeless powder base which is at at least partially miscible with the suspending medium and is mixed with a volatile liquid non-solvent which is substantially miscible therewith and reduces the solubility of the suspending medium in the solvent, and thereafter removing the vehicle from the lacquer globules while they are thus suspended.

References Cited in the file of this patent 

1. IN THE MANUFACTURE OF POWDER GRAINS BY DISPERSING GLOBULES OF SMOKELESS POWDER BASE LAQUER IN A NONSOLVENT MEDIUM, THE PREOCESS OF REDUCING THE QUANTITY OF NON-SOLVENT MEDIUM DISPERSED WITHIN SAID GLOBULES WHICH COMPRISES INCLUDING IN THE LACQUER A VOLATILE LIQUID NONSOLVENT DILUENT WHICH IS SUBSTANTIALLY MISCIBLE WITH THE LACQUER SOLVENT AND SUBSTANTIALLY IMMISCIBLE WITH THE NON-SOLVENT MEDIUM. 